Endorphins are neuropeptides produced by the pituitary gland and central nervous system that act as natural pain killers and mood elevators. They bind to opioid receptors in the brain, producing feelings of pleasure and reducing pain perception.
Sustained aerobic exercise — typically after 20–30 minutes of moderate-to-vigorous activity — triggers endorphin release, often described as 'runner's high'. Research suggests this effect is also partially mediated by endocannabinoids (similar to cannabis in effect), which may better explain the mood-calming, not just euphoric, aspects of post-exercise wellbeing.
A 2016 meta-analysis in The Lancet Psychiatry (290,000 participants) found that regular exercise was associated with significantly fewer poor mental health days. Exercise has been shown to be as effective as antidepressants for mild-to-moderate depression in some studies, with effect sizes improving with longer duration programmes.